The invention relates generally to bullet cartridges for hand-held guns. In particular, the invention relates to disk cartridges that deform into elongated projectiles during ejection from a tapering gun barrel.
Shortly after World War II (WWII), the U. S. Army studied the capabilities of the infantry rifle, hit probability a function of range, the typical ranges encountered in battle, and the wound effects of hits with differing ballistic characteristics. These studies led to conclusions that:
(1) hit probability with the M1 rifle was satisfactory only up to 100 yards, declining rapidly beyond that;
(2) 300 yards was the range limit for most combat rifle engagements;
(3) a pattern-dispersion principle in the hand weapon could compensate for human aiming errors and increase hit probability within combat ranges; and
(4) bullets smaller than 0.30 caliber could be used without loss in wound-effectiveness and with logistical advantage.
Since WWII, the U.S. Army has endeavored to significantly increase the lethality of combat rifles by improving hit probability (Ph) and ammunition capacity through innovative rifle designs and ammunition concepts. Initial studies done under the s indicated that rifles of the time were ill-suited to typical combat environments and urged the development of rifles that increased hit probability via controlled bursts. This concept was first pursued by the Army under Salvo and Salvo Squeeze-bore programs used multi-projectile concepts to improve hit probability. Later work included the Special Purpose Individual Weapon program to create a rifle with twice the hit probability of the M14, and later with the Advanced Combat Rifle program's effort to create a rifle with higher hit probability and twice the capacity of the M16. Neither program succeeded.
Later service rifle development shifted away from those goals until the Army's recent Light Small Arms Technologies program's caseless cartridge research. Thus, the Army's service rifle hit probability and capacity requirements remain unmet. Meeting these needs will call for a much lighter, smaller cartridge than the 5.56×45 currently in service. In 1948, the Army's newly-organized Operations Research Office (ORO) studied three million casualty reports from both World Wars during their ALCLAD armor project. The ORO concluded that most combat occurred within a range of 300 yards, with opposing combat teams encountered each other unexpectedly, and those forces with greater firepower tended to win. The ORO also found that hits were often random and that beyond 100 yards marksmanship was reduced by terrain and visibility. Thus time and target exposure were the biggest factors for hit probability, and the main predictor of casualties was the total number of rounds fired.
Influenced by ALCLAD's wound ballistic research, ORO and the Army's Ballistics Research Laboratory (BRL) began a study of combat rifle effectiveness. ORO concluded that infantry should be equipped with a fully-automatic rifle to increase rate-of-fire (ROF), while BRL concluded that a smaller caliber rifle could give greater terminal performance while increasing hit probability at shorter ranges. These conclusions suggest that an ideal service rifle for the US armed forces would be smaller caliber, capable of rapid fire rifle, and with twice the hit probability of existing rifles. The increased hit probability could be achieved either by more accurate fire, or through controlled bursts.
ORO concluded that a rifle designed to provide controllable bursts within a 300-yard range might be preferable to a weapon that provides precise single shots at longer distances. The key was controllability, because an uncontrolled automatic weapon was determined to be no more advantageous than a semi-auto rifle. The ORO projected that a four-round salvo with a 20″ spread could double the 300-yd hit probability of a single shot from an M1 rifle. On the downside, such weapons clearly increased ammunition use. Thus in order for a soldier to carry enough ammunition for a firefight, cartridge mass would have to be significantly reduced. The smaller caliber cartridges might also be light enough to enable an equivalent number of fired salvos as compared to the individual cartridge capacity of the M1, making the soldier armed with the smaller caliber twice as effective as when armed with an M1.
Increase in hit probability could be accomplished by controlled bursts. The controlled burst concept led to Project SALVO beginning 1952, which studied the hit probability of multi-shot bursts and later project Salvo Squeeze-bore (SSB) in 1962. Two notable test entries were BRL's modified M2 carbine firing triplex loads from a 0.224 cartridge and 12-gauge shells from the Office of Naval Research (ONR) firing thirty-two steel flechettes. The resulting tests, beginning in June 1956, found that multi-shot loads provided higher hit probability than the M14. However, there remained many engineering problems preventing the multiple loads from becoming practical. The alternative to multi-shot loads were high ROF bursts of single-shot cartridges. A 1961 BRL test demonstrated that 2300-rpm bursts increased hit probability by 10% to 270% over a similar length full-auto burst from an M14. Both of these options would continue to be pursued under later projects described subsequently.
Concurrent with Project Salvo, a commercial 5.56×45 mm rifle was being developed by Armalite Corporation, influenced by the ORO and BRL rifle effectiveness studies. In 1958 the Army found that the lighter and smaller AR-15 could be brought to bear quicker than other existing rifles, concluding that an eight-man team with AR-15's would have the same firepower as an eleven-man team armed with the M14. After a successful 1960 demonstration of the AR-15, the Strategic Air Command ordered 8,500 AR-15s. The Advanced Research Projects Agency bought a thousand more AR-15s—now called the M16—for South Vietnamese troops in 1962.
American soldiers and advisors working with the South Vietnamese encouraged use of the M16 by U.S. soldiers. As a replacement for the M1 and M14 was needed, and because the research and development (R&D) for such a replacement remained underway, the M16 was the best option available. The M16 did not meet the capabilities requirements for hit probability and burst rate first identified in Army rifle requirements studies of the 1950's. The pursuit of this capability would continue under future projects until 1992 and again in the current Light Small Arms Technology (LSAT) program.
Since 1952, the U.S. Army has conducted a series of R&D programs with the goal of creating an infantry rifle with higher hit probability and ammunition capacity than the M14 and M1 rifles available fifty years ago. This research was initiated by several post-World War II studies, which indicated that the rifles used exhibited inadequate hit probability for the battlefield environments actually encountered. The inadequacies of existing rifle technology could be mitigated by using automatic burst-capable rifles designed to provide improved hit probability while being light enough to carry. This was confirmed by Project Salvo (1952-1962), which investigated multi-shot bursts and their effect on hit probability. By 1962, the M16—firing the 5.56×45 cartridge—has been adopted as the standard U.S. service rifle, replacing the M14.
The 5.56×45 cartridge is rimless bottlenecked standard cartridge for North Atlantic Treaty Organization (NATO) countries, and derives from the 0.223 Remington cartridge. The 5.56×45 cartridge has a total length of 5.74 cm firing a projectile having a diameter of 0.57 cm and a length of 1.21 cm. The 5.56×45 cartridge with 62 grains has a mass of 4.0 grams. However, because the M16's three-round bursts did not provide a close enough shot distribution for increased hit probability, the M16 did not satisfy the requirements of the original research programs that brought about the development of an improved battle rifle in the first place.
With the results from Projects Salvo and Squeeze-bore, the Army conducted the Special Purpose Individual Weapon (SPIW) program (1962-1973) with the objective of developing a rifle with twice the hit probability of the M14. Although the SPIW program ended unsuccessfully some promising concepts from this program, which were further developed under follow-on programs, including the Future Rifle Program (FRP) and Future Rifle Systems (FRS) programs. Later the Advanced Combat Rifle (ACR) Program (1987-1992) picked up where the SPIW program left off, seeking to double the hit probability and ammunition capacity of the M16, which had been adopted just at the opening of the SPIW program for the Advanced Combat Rifle (ACR). However, none of the entries met the program's performance requirements, likely due to the hit physical limitations of the brass-cased cartridge paradigm. Thus, the guidelines laid out early on by ORO the SPIW program and pursued up through the ACR program-guidelines detailing real needs of the Army-remain unmet.
In 1961 the Army's Combat Development Experimentation Command (CDEC) published the study “Optimum Composition of the Rifle Squad & Platoon”, which suggested that members of a squad should be armed with flechette rifles. In 1962, based on CDEC's report, the Ordnance Corps began the Special Purpose Individual Weapon (SPIW) program to develop an automatic rifle carrying sixty flechettes and three grenades while weighing under 10-lb per soldier-load. By February 1963, Phase I contracts were awarded to Aircraft Armaments Inc., (AAI), Springfield Armory, Harrington & Richardson (H&R), and Winchester.
The prototypes submitted by AAI, Springfield, and Winchester all used specially designed saboted single-flechette cartridges, while and H&R used a saboted triplex cartridge of its own design. Ultimately, all four entries were deemed too heavy, too complicated, or unreliable for further development. After an unsuccessful Phase I, the SPIW program continued with the Serial Flechette Rifle project. In February 1967, AAI was funded by BRL to improve their SPIW flechette rifle. By November 1967, however, the preexisting issue of rapid heating resulted in actual occurrences of cartridge cook-offs (earlier prototypes were not fired long enough to for cook-off to occur). Thus AAI turned their focus on to eliminating the cook-off problem, which was eventually achieved.
The pursuit of a combat rifle meeting the performance levels laid out originally for Project SALVO continued throughout the 1960's and 1970's. In 1969 the FRP sought to further develop AAI's flechette rifle, with a focus on multiple flechettes per cartridge. Springfield Armory's SPIW design was also pursued. However, by December 1973, flechette ammunition was removed altogether from “immediate consideration” in the upcoming FRS Program, due to problems with the sabot cartridge.
In 1988, the Army began the Advanced Combat Rifle (ACR) program to produce a service rifle with the loftier goal of doubling the hit probability and ammunition capacity available in the now standard M16, which had a hit probability of 20% at 100 meters (m), 10% at 300 m, and 5% at 600 m. This was a tighter requirement then that of the old SPIW program which sought to improve on the older M14 while maintaining a per-soldier load of under 10-lb. Four contracts were awarded for the ACR program: AAI, Heckler & Koch (H&K), Steyr, and Colt. Ultimately, none of the entries offered a large enough capacity or enough of a hit probability increase over the M16A2 to warrant further development or adoption. After the ACR program ended in 1992, service rifle development work shifted from efforts to double hit probability and ammunition capacity to focus on indirect fire systems. In 1993, the Army initiated the Objective Individual Combat Weapon (OICW) to develop a rifle capable of attacking targets behind cover by using airburst munitions.
The OICW program's focus was refined to a combination of a short assault and semi-automatic, low-velocity 20 mm-to-25 mm cannon firing air-bursting munitions. The winner of the OICW contract was the Alliant Techsystems XM29, which included an advanced programmable 20 mm grenade launcher, but was based on an existing rifle design firing the 5.56×45 cartridge. The OICW program was cancelled and the XM29 shelved in 2004, while the rifle portion of the XM29 was continued as the XM8 program until cancelled in October 2005. The efforts to produce a rifle with double the hit probability and ammunition capacity of the M16 and previous rifles remain unsuccessful.
The most advanced cartridge technologies under active development are the caseless and plastic-cased “telescoping cartridges” of the Lightweight Small Arms Technology (LSAT) program at the Army Research Development and Engineering Center (ARDEC). The goal of this program is a 50% reduction in mass and 40% reduction in volume per cartridge, relative to the 5.56×45 SS109 and M855 cartridges. The LSAT Program is pursuing two cartridge designs-a polymer-cased telescoped round by ARES and a caseless round (by ATK) based on HK G11 technology. This program is also developing a larger caseless cartridge for use in a potential machinegun replacement for both 5.56×45 and 7.62×51 caliber machine guns. The goal of the machine gun effort is to produce a machine gun with the weight of the 5.56 mm while maintaining the effectiveness of the 7.62×51 cartridge.
The state of the art as relates to combat rifles and ammunition is represented by those developed most recently in the ACR program—primarily the H&K G11 rifle and its 4.7×33 caseless cartridge, and secondarily the Steyr ACR's plastic-cased flechette cartridges. The H&K 4.7×33 caseless cartridge represents the state of the art with respect to caseless ammunition and solid propellants, and is capable of withstanding 100° C. higher chamber temperatures before “cook-off”. This results in a round that has been incorporated into a light machinegun design rated for 300-rounds before overheating. This rifle also appears to most closely approach the requirements for the necessary burst speeds and ammunition capacity, firing 2000-rpm three-round delayed-recoil bursts from a 45-round magazine.
However, the burst rate falls short of the 2400-rpm rate indicated in “Operational Requirements for an Infantry Hand Weapon” and the magazine capacity still falls short of the 60-rounds specified by the ACR program requirements. The Steyr ACR flechette cartridges were also very low mass, with the added advantage of velocities as high as 1500-m/s a flattened trajectory, and long range due to the low drag of the flechette. The Steyr ACR cartridges achieved low mass not by eliminating the case, as with the G11, but by using a polymer case and by using a very light 10-grain projectile.
Another recent innovative development in small arms ammunition is a superposed load system by Metal Storm Ltd. of Brisbane, Australia, capable of firing 30,000-rpm bursts from a single barrel. This system involved multiple cartridges loaded in a single barrel (eliminating the magazine and action) and fired, electronically one at a time. Such a system enables extremely high rate-of-fire bursts as well as individual shots. This system, however, does not enable high ammunition capacity through low per-round weight and is thus better suited for specialized applications, such as less-than-lethal weapons, grenade launchers, and closein-defense weapons. However, because the Metal Storm system relies on larger ammunition and is limited to the space within the barrel—or barrels—Metal Storm will likely lack the operating characteristics and ammunition capacity required for service rifles.
Two notable innovations, flechettes and caseless propellants, provide incremental advantages, but have thus far fallen short of meeting U.S. military requirements. While caseless cartridges reduce mass and increase firing rate by eliminating the metallic case, they have not sufficiently increased hit probability and capacity, and have also raised durability concerns due to the exposed propellant. Flechettes achieve high velocity with low recoil and low mass due to lighter projectiles, but have been plagued by cost and safety concerns. The challenge is to draw on these concepts such that their individual pitfalls are avoided.